Derek
<group id="test" caption="Test">
<insertButtonPalette refID="esri_task_insertMenu" size="middle"/>
</group>
and
<group id="test" caption="Test">
<buttonPalette refID="esri_task_insertMenu" size="middle"/>
</group>
are exactly the same. You can do either. Mostly we use the tag without the insert prefix. Sorry for the confusion.
re the ids of "esri_task_xxx" vs "esri_tasks_xxx". This was a typo in our source code with respect to consistency. Good pickup.
When you define a button / tool / menu / etc. the key attribute is "id". Internally at Esri we use a particular naming convention of "esri_(modulename)_xxx". We recommend a similar pattern for add-in developers of (moduleName)_xxx, but the id string can be anything. The important thing is it must be unique within your module.
Any item in groups, tabs, menus etc that use a "refID" attribute must have a corresponding entry in the <controls> section of the combined ArcGIS Pro daml file that defines that id. In this way, you have the ability to reference any of our Esri daml buttons, tools, menus etc in your add-in not just those defined by you.
Regards
Narelle